Method of producing refractory metals



United States Patent 4 METHOD OF PRODUCING REFRACTORY METALS James L. Vaughan, Needham, Mass., assignor to National Research Corporation, Cambridge, Mass, a corporation of Massachusetts Filed Dec. 30, 1954, Ser. No. 478,652

2 Claims. (Cl. 75-84J) This invention relates to the production of metals and more particularly to the production of refractory metals such as titanium and the like. In the previous application of Keller et al., Serial No. 434,648, filed June 4, 1954, now Patent No. 2,846,304, granted August 5, 1958, there is described a process for the production of titanium in which high yields of large crystals of titanium are obtained by the two-stage reduction of a titanium halide. It is a principal object of the present invention to pro vide an improved apparatus and process particularly adapted for utilization with the invention described in the above Keller et al. application.

Another object of the invention is to provide an im proved process for speeding up the operation of the second stage reduction without impairing the yield of i high-quality metal.

Still another object of the invention is to provide an improved apparatus which is particularly adapted to largcscale commercial production of high-purity metal.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such of such steps with respect to each of the others, and the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

Fig. l is a diagrammatic, schematic view of one preferred embodiment of the invention; and

Fig. 2 is a diagrammatic, schematic view of another preferred embodiment of the invention.

In the present invention, the refractory metal compound is dissolved in a fused salt and is reduced to the refractory metal in the form of relatively large crystals by means of a liquid metal reducing agent. In a preferred embodiment of the invention, the refractory metal compound is a titanium halide so that titanium crystals are the end product. The present invention also preferably includes a two-stage reduction of the titanium halide to first produce a solution of titanium lower halides in a fused salt such as sodium chloride. The titanium halide dissolved in the molten salt is then preferably reduced to metallic titanium by means of a reducing agent which is sprayed across the surface of the solution. This reducing agent is preferably sodium and the invention will be described in connection with the utilization of sodium as the reducing agent, titanium lower chlorides as the titanium halide, and sodium chloride as the fused salt.

The present invention is particularly directed to improvements in apparatus and techniques for accomplish- "ice ing the second stage reduction. As pointed out in the Keller et al. application, it is highly desirable to so conduct the second stage reduction that sodium is uniformly sprayed across the surface of a solution of titanium dichloride in fused sodium chloride. As a result of this spraying, a crust of fine particles of titanium forms at the surface of the fused salt. This crust has some mechanical strength due to the sintering of the fine titanium particles to each other, but the crust is preferably supported every few inches or so by means of a suitable grid or the like, this grid being helpful in preventing collapse of the crust in later stages of the titanium crystal growth. As more sodium is fed to the salt bath, the level of the salt tends to rise above the crust due to the formation of more sodium chloride. During this further feed of sodium, tanium crystals grow from the bottom of the crust to form an interlaced mass of relatively large titanium crystals, many of which have dimensions on the order of an inch or so. During the latter part of the reduction operation, it has been discovered that the rate of entry of sodium into the bath slows down. The reason for this is not fully understood, but it is believed that the titanium crust, even though it does not appreciably increase in thickness during the course of the reduction, somehow interferes with the transfer of sodium from the surface of the bath down into the deeper portions of the bath where unreduced titanium dichloride solution is present. It has been discovered that periodically rupturing the crust in limited portions thereof at later times in the second stage reduction greatly increases the entry of the sodium into the fused salt bath so as to increase both the utilization of sodium and the percentage of titanium dichloride which is reduced to crystalline titanium of large particle size.

In one preferred apparatus for practicing the present invention, the second stage process is carried out in a plurality of individual reactors which are loaded with a solution of titanium dichloride in sodium chloride. Sodium is then preferably sprayed onto the surface of the solution at a controlled rate over a long period of time to form an initial layer of titanium crust adjacent the surface of the molten salt. The reactor includes a crust-supporting structure and a means for periodically rupturing limited portions of the titanium crust, particularly near the end of the second stage of the reduction. In one embodiment of the invention, the second stage reactors comprise individual pans which are advanced through a long air-free oven, the pans passing a plurality of stations for feeding of sodium to the surface thereof and at least one station for piercing the crust. In a preferred arrangement of this embodiment of the invention, the by-product salt is separately dumped from the pan, the great bulk of the titanium crystals being held in the pan by a crust-supporting structure. This permits rapid cooling of the titanium crystal mass so that residual sodium chloride can be readily removed by slightly acidified cold water.

Referring now to the drawings, there is indicated schematically one embodiment of the invention wherein titanium tetrachloride is partially reduced by sodium to form a solution of titanium dichloride in sodium chloride in a first stage reactor 10. A portion of this solution is transferred by means such as a pipe 12 to one of a plurality of second stage reactors 14 which are advanced in a stepwise fashion through an oven 16. The second stage reactors 14 are preferably in the form of individual pans which are preferably introduced into the oven 16 by means of a loading chamber 18 arranged to prevent access of air and other contaminating gases to the interior of the oven 16. For this purpose, the

oven is preferably maintained at a slight positive pressure of argon. Suitable locks are also preferably provided to permit a partial or complete evacuation of the loading chamber 18 and of an unloading chamber 20 to assist, if necessary, in the prevention of entrance of air into the oven 16. Alternatively, the loading and unloading chambers can be at a higher inert-gas pressure than the oven to prevent outward diffusion of sodium vapors and the like. In this case, these two chambers 18 and 20 are preferably kept at a superatmospheric pressure of argon. Sodium is preferably sprayed onto the surface of the salt solution in the pans as they are advanced through the oven 16, the sodium being sprayed at a relatively slow rate so as to initially form a thin, sintered titanium crust adjacent the surface of the bath and then to accomplish gradual reduction of the average valence of the titanium content of the salt solution. As the pans advance through the oven 16, they are passed under at least one crust-breaking mechanism, indicated as a plurality of pointed rods 23, these rods being shown in greater detail in Fig. 2. These rods are for the purpose of breaking limited portions of the titanium crust adjacent the surface of the fused salt mixture. From the crustbreaking station, the individual pans are transferred, after completion of the reduction reaction, to a dumping station where the bulk of the molten salt 26 is dumped from the pans into a suitable salt removal mechanism indicated at 25, which can be provided at the bottom of a well 24 in a portion of the oven 16. Dumping of the bulk of the salt from the titanium crystals provides a much smaller mass of material to be cooled and consequently speeds subsequent processing operations. After the salt has been dumped, the pans may be transferred to the unloading chamber 20.

Referring more specifically to Fig. 2, there is shown an enlarged fragmentary, sectional view of one of the pans 14 illustrating the crust-breaking operation. In this Fig. 2, the molten salt is shown at 26, this salt is confined by pan 14 which also includes a grid which supports a titanium crust 42 adjacent the surface of the salt at the beginning of the second stage reduction. As pointed out previously, during the reduction the increased production of by-product sodium chloride furnishes a layer 26a of by-product salt above the crust 42. Sodium, as mentioned previously, is preferably fed to the surface of the layer 26:: during further reduction. The crust breakers 23 are shown in a retracted position after having punctured the crust 42 by pushing small segments 42a thereof down into the mass of titanium crystals carried on the under surface of the crust. This permits relatively free communication between the layer of salt 26a above the crust.42 and the bulk of the salt 26 below the crust. The presence of the holes in the crust also facilitates the passage of the molten salt through the crust when the salt is drained from the reactor 14 at the end of the second stage reduction.

Numerous alternative methods of practicing the pres ent invention may be employed. For example, the temperature of the reaction mass may be widely varied from slightly above the inciting point of the salt to temperatures on the order of 1000 C. and above. Numerous reducing agents other than the sodium can be employed, for example, potassium, calcium, magnesium, lithium and various combinations of these elements may be utilized. From the standpoint of cheapness, sodium, sodium-potassium alloy or magnesium are preferred. Other halides of titanium may be utilized, although, from the standpoint of cost, ease of handling, etc., the tetrachloride is pre ferred.

Additionally, the reactor can be fed with lower halides of titanium such as titanium trichloride manufactured from titanium-bearing materials in the manner shown in the copending applications of Singleton, Serial No. 304,- 388, filed August 14, 1952, and Singleton, Serial No.

315,461, filed October 18, 1952. Equally, titanium trichloride can be made by the technique described by Sherfey et al., Journal of Research of the Bureau of Standards 46, 299-300, April 1951. Additionally, the dichloride of titanium can be manufactured by numerous processes such as disproportionation of the trichloride or partial reduction of the trichloride or tetrachloride.

The present invention can be equally employed for the manufacture of titanium alloys by the coreduction of the chlorides, for example, of zirconium, vanadium, chromium, manganese, iron, nickel, cobalt, columbium, tantalum, molybdenum, tungsten or silicon. The alloy may be a binary alloy or it may be an alloy containing three or four constituents. In the manufacture of al loys, the same general conditions of the reduction of the titanium halide and reducible compounds of the alloying constituents must be employed. Accordingly, when used in the claims, the word titanium is intended to mean alloys thereof as well as the pure metal.

While the invention has been particularly described in connection with the production of titanium, it is also applicable to the production of other refractory metals such as zirconium, thorium, vanadium, columbium, tungssten, tantalum, molybdenum and the like by the reduction of reducible compounds such as the halides of such refractory metals dissloved in suitable fused salts. It should be additionally pointed out that the salt mixture in which the reduction is carried out may be formed of numerous halides which can be mixed halides, single halides and halides of materials other than the specific reducing agent or agents employed in the reaction. From the standpoint of simplicity of operation and ease of control, however, it is preferred that the salt be the chloride of the reducing agent. It is quite feasible to employ binary and ternary mixtures of halides having quite low melting points.

It should be pointed out, in connection with a consideration of the various salts which can be employed, that these salts should be completely anhydrous and free of any contaminants such as carbon, nitrogen, oxygen or hydrogen. This is particularly true when making metals such as titanium due to the tremendous reactivity of. titanium metal at temperatures on the order of 800 C. to 900 C. and above.

In the above specification, reference has been made particularly to the preferred titanium chlorides, tetrachloride and dichloride. In most instances, the trichloride is equally useful and, as a matter of fact, it is extremely unlikely that any system having an appreciable concentration of one of the lower chlorides of titanium will not have at le st some of the other lower chloride also present. It should be apparent that one can also employ the corresponding di-, tri-, and tetrahalides from the group consisting of the iodides, bromides and fluorides of titanium.

Since certain changes may be made in the above process and apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawing, shall be interpreted as illustrative, not in a limiting sense.

What is claimed is:

1. In a process for manufacturing a refractory metal from the class consisting of titanium, zirconium, thorium, vanadium, columbium, tungsten, tantalum and molybdenum wherein a halide of the refractory metal is dissolved in a molten salt and is reduced to refractory metal by means of a liquid metal reducing agent selected from the class consisting of lithium, sodium, potassium, magnesium and calcium and mixtures thereof, the molten salt comprising at least one halide selected from the class consisting of the alkali metal halides and the alkaline earth metal halides, the improvement which comprises providing a crust of sintered refractory metal particles in the upper portion of the bath and adjacent the surface of the molten salt bath, said crust being substantially coextensive in area with the bath surface, and serving as a sup port for crystals of said refractory met-a1 growing from the bottom of the crust, supporting the crust at spaced points so that it is held under the bath surface and immediately adjacent to the bath surface, feeding reducing agent to the upper surface of the molten salt bath above the crust, continuing the support of the crust adjacent the surface of the salt bath during reduction of refractory metal halide within the salt bath, and periodically rupturing limited portions of the crust during latter stages of the reduction to assure substantially complete reduction of the dissolved refractory metal halide.

2. The process of claim 1 wherein the refractory metal halide is a lower chloride of titanium and the crust is ruptured by punching holes through the crust between the points of support.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,148,345 Freudenberg Feb. 21, 1939 2,564,337 Maddex Aug. 14, 1951 2,586,134 Winter Feb. 19, 1952 2,607,674 Winter Aug. 19, 1952 

1. IN A PROCESS FOR MANUFACTURING A REFRACTORY METAL FROM THE CLASS CONSISTING OF TITANIUM, ZIRCONIUM, THORIUM, VANADIUM, COLUMBIUM, TUNGSTEN, TANTALUM AND MOLYBDENUM WHEREIN A HALIDE OF THE REFRACTORY METAL IS DISSOLVED IN A MOLTEN SALT AND IS REDUCED TO REFRACTORY METAL BY MEANS OF A LIQUID METAL REDUCING AGENT SELECTED FROM THE CLASS CONSISTING OF LITHIUM, SODIUM, POTASSIUM, MAGNESIUM AND CALCIUM AND MIXTURES THEREOF, THE MOLTEN SALT COMPRISING AT LEAST ONE HALIDE SELECTED FROM THE CLASS CONSISTING OF THE ALKALI METAL HALIDES AND THE ALKALINE EARTH METAL HALIDES, THE IMPROVEMENT WHICH COMPRISES PROVIDING A CRUST OF SINTERED REFRACTORY METAL PARTICLES IN THE UPPER PORTION OF THE BATH AND ADJACENT THE SURFACE OF THE MOLTEN SALT BATH, SAID CRUST BEING SUBSTANTIALLY COEXTENSIVE IN AREA WITH THE BATH SURFACE, AND SERVING AS A SUPPORT FOR CRYSTALS OF SAID REFRACTORY METAL GROWING FROM THE BOTTOM OF THE CRUST, SUPPORTING THE CRUST AT SPACED POINTS SO THAT IT IS HELD UNDER THE BATH SURFACE AND IMMEDIATELY ADJACENT TO THE BATH SURFACE, FEEDING REDUCING 